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Full text of "Treatise On Applied Analytical Chemistry(Vol-1)"

140

LIMESTONES AND  MARLS

the substance after treatment with hydrochloric acid, or on the increase
in weight of an apparatus for absorbing the carbon dioxide1 generated.

Various forms of apparatus have been designed to determine the loss
of weight, one of the most simple1 being that shown in Fig. 5. It consists
of a flask with a, doubly-bored stopper, through which pass (i) a bulb tube
a furnished with a cock and drawn out at the- bottom, and (2) a delivery
tube terminating in a wider lube t> containing granulated calcium chloride
and a little fused borax. Into the weighed flask a definite weight (about
I gram) of the substance is introduced, together with a, few c.e. of water,
the bulb being tilled with dilute hydrochloric acid and the upper ends of
tubes a and /; closed by rubber tubing and glass rod
plug or clip. The whole is Utted together so that all
the joints are air-tight and weighed. The upper ends
of a and b are then opened and the hydrochloric add
allowed to flow gradually into the ila.sk, a, slow cur-
rent of air being drawn through the apparatus from
a to l>. The tube- ti is next closed and the llask
heated gently on a water-bath and afterwards allowed
to cool. Dry air is again passed through the1 appar-
atus for a, lew minutes, the tubes then closed, and the
whole weighed, the loss in weight giving the carbon
dioxide in the substance taken.

More accurate is the determination of the carbon
dioxide- by the increase in weight of an absorption
apparatus. This is effected by introducing a.n exact
amount of the substance (about i gram) into a, llask,
adding a little water and closing the tla.sk with a
two -lulled stopper, through which pass a. reflux con-
denser and a safety tube leaching almost to the
bottom of the llask and terminating al the upper
end in a tap which can be connected either with a
funnel or with a. potash, apparatus for purifying the.
air from carbon dioxide. The reflux condenser com-
municates with a LHulx- charged with glass beads
and concent .rated sulphuric acid, beyond which conic
first an absorption apparatus consisting of two
weighed LHubes containing soda lime and then an
aspirator. Dilute hydrochloric, acid is poured on to the substance by
means of the funnel, the. tap being then closed and the tunnel removed,
Connection is next made with the potash apparatus, the, lap being opened,
the aspirator started gently and the flask gradually heated to boiling.
Air is passed for at least 15 minutes after heating is discontinued, the
absorption tubes being then disconnected and weighed, the carbon dioxide
in the substance; being thus determined.

If it is likely that the substance contains sulphides, it is well, before
the reaction, to add a little meicurie chloride solution to re-tain the hydrogen
sulphide.

(b) GASOMISTIUC METHOD.    One of the best known forms of apparatus

entation and distil-